How this game works is that each poster (you can post multiple times) names two things that exist in the world of Shiibah which are added to the positive list, and two things that do not which are added to the negative list.

Specific trumps general. If a previous poster puts "dinosaurs" on the positive list, you can put "t-rex" on the negative list. This means that the world has dinosaurs in general, but is missing the t-rex in particular. Likewise if "t-rex" is already on the positives, then you can't put "dinosaurs" on the negatives. (You could, however, put "any type of dinosaur other than t-rexes")

I'll start and try to keep this post updated as the game goes (if it goes):